In recent years, a semiconductor memory (e.g. NAND flash memory) has been applied to various memory systems, and accordingly there has been a challenging how to increase the memory capacity thereof. To achieve this, memory chips are mounted in a storage device, and multilevel configuration, for instance, is adopted, thereby to realize a large memory capacity. In such a storage device, memory chips are controlled by a memory controller.
However, in a memory system (semiconductor memory system) using the semiconductor memory, it is difficult to increase the speed. This is conspicuous in a semiconductor memory with a fine structure, or a multilevel semiconductor memory. Thus, the memory controller executes control to perform data program operations in parallel in memory chips.
When program operations are executed in parallel, is an overlap of peak periods of electric currents consumed in the respective memory chips. If the peak periods of consumption currents of the memory chips overlap, a very large current is temporarily consumed in the semiconductor system, and this adversely affects other parts, leading to degradation in capability of the semiconductor system.